map-dots/imaging/circles.go

package imaging

import (
	"fmt"
	"image"
	"math"

	"git.fjla.uk/fred.boniface/map-dots/data"
	"git.fjla.uk/fred.boniface/map-dots/log"
	"github.com/fogleman/gg"
)

func mapCirclesToCanvas(img *image.RGBA, locations []data.LocationData) {
	log.Msg.Debug("Mapping locations to canvas")
	dc := gg.NewContextForRGBA(img)
	dc.SetRGB(1, 1, 1) // Set canvas background color (white in this case)

	circleRadius := 4 // Replace with your desired fixed radius

	bounds := img.Bounds()
	canvasWidth := bounds.Max.X - bounds.Min.X
	canvasHeight := bounds.Max.Y - bounds.Min.Y

	var minLat, maxLat, minLon, maxLon float64
	for _, loc := range locations {
		if loc.Latitude < minLat {
			minLat = loc.Latitude
		}
		if loc.Latitude > maxLat {
			maxLat = loc.Latitude
		}
		if loc.Longitude < minLon {
			minLon = loc.Longitude
		}
		if loc.Longitude > maxLon {
			maxLon = loc.Longitude
		}
	}

	centerLat := (maxLat + minLat) / 2.0
	centerLon := (maxLon + minLon) / 2.0
	latRange := maxLat - minLat
	lonRange := maxLon - minLon

	for _, loc := range locations {
		pixelX, pixelY := convertCoordinatesToPixels(loc.Latitude, loc.Longitude, centerLat, centerLon, latRange, lonRange, canvasWidth, canvasHeight)

		// Draw the circle on the canvas using gg
		dc.DrawCircle(float64(pixelX), float64(pixelY), float64(circleRadius))
		dc.SetRGBA(1, 1, 1, 0.5) // Circle fill color (white with 50% opacity)
		dc.Fill()
	}

	dc.Clip() // Apply clipping

	// Optional: Save the canvas as an image file
	err := dc.SavePNG("output.png")
	if err != nil {
		log.Msg.Error("Error saving file")
	} else {
		fmt.Println("Canvas saves to file")
	}
}

func convertCoordinatesToPixels(latitude, longitude float64, centerLat, centerLon, latRange, lonRange float64, canvasWidth, canvasHeight int) (int, int) {
	// Calculate normalized latitude and longitude distances from the center
	latDist := (latitude - centerLat) / (latRange * 0.5)
	lonDist := (longitude - centerLon) / (lonRange * 0.5)

	// Calculate the maximum distance from the center as a proportion of canvas size
	maxDistance := math.Max(math.Abs(latDist), math.Abs(lonDist))

	// Adjust the normalized distances to match the canvas size with margins
	adjustedLatDist := latDist / maxDistance * 0.45
	adjustedLonDist := lonDist / maxDistance * 0.45

	// Calculate pixel positions
	pixelX := int((adjustedLonDist + 0.5) * float64(canvasWidth))
	pixelY := int((0.5 - adjustedLatDist) * float64(canvasHeight))

	return pixelX, pixelY
}